This invention relates to forage harvesters of the type having a basic processing unit and a gathering unit attached thereto for vertical swinging movements about a transverse axis on the basic unit frame and, more particularly, to an apparatus for controlling the swinging movements of the gathering unit.
Conventional forage harvesters are provided with gathering units which are designed to follow the ground by pivoting about a transverse axis on the frame of the basic processing unit. The gathering unit control apparatus in most units includes a transverse rockshaft pivotally mounted on the basic unit having a lifting lever which extends under the gathering unit and one or more levers to which a counterbalancing or floatation spring and lifting cable or hydraulic cylinder may be attached. Such a control apparatus is illustrated for example in Waldrop U.S. Pat. No. 3,355,865. In such systems, the force of the floatation springs are generally adjusted by a screw or crank mechanism. Commercial systems have been built having a means for locking out the lift linkage for transport. Moreover, since it usually requires additional downward movement of the lifting lever for picking up the gathering unit, it is desirable for the floatation springs to be relaxed during this operation. This has previously been accomplished by backing off the spring adjusting screws or cranks. Some machines have been built wherein the floatation springs are fully relaxed in the transport position and could be removed from the system for pickup. However, over the range of vertical travel of the gathering unit, the floatation springs go from a zero counterbalancing condition to a maximum counterbalancing condition and the lowest operating position of the gathering unit. In the linkage described and claimed herein, when the gathering unit is in the transport position, the floatation springs provide a counterbalancing of significant proportion compared to the maximum counterbalancing force, yet this force may be relieved for picking up the gathering unit without disturbing the spring adjustments.
Yet another aspect of controlling the gathering unit is the nature of the loading imposed on the basic unit frame. In some commercial machines, the unit lifting lever is a single member generally offset to one side of the gathering unit. Others have two lifting levers. However, by attaching the lift levers to a cross tube mounted on the frame, if the loading on the gathering unit is unequal, the loading on one side or the other of the frame, both at its pivot connections therewith and at its lifting connection therewith will be unequal. If a pair of balancing springs are used on each side of the crop passage, one spring will experience a greater loading under these conditions. In the invention described herein, a single tension member is used having its ends connected to the gathering unit on either side of the housing and its medial portion looped around a movable pulley attached to the lifting floatation means. The effect of this is to equalize the loading on the frame caused by the lift system.